Diagenesis

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  • Diagenesis
definition
  • The physical and chemical change undergone by sediment during lithification and compaction.  
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broader
Abstract from DBPedia
    Diagenesis ( ) is the process that describes physical and chemical changes in sediments caused by increasing temperature and pressure as they get buried in the Earth's crust. In the early stages, this transformation of sediment into sedimentary rock (lithification) is accompanied simply by a reduction in porosity, while its component mineralogy remains unaltered. As the rock is carried deeper by further deposition above, its organic content is transformed into kerogens and bitumens. The process of diagenesis excludes surface alteration (weathering) and metamorphism. There is no sharp boundary between diagenesis and metamorphism, but the latter occurs at higher temperatures and pressures. Hydrothermal solutions, meteoric groundwater, porosity, permeability, solubility, and time are all influential factors. After deposition, sediments are compacted as they are buried beneath successive layers of sediment and cemented by minerals that precipitate from solution. Grains of sediment, rock fragments and fossils can be replaced by other minerals during diagenesis. Porosity usually decreases during diagenesis, except in rare cases such as dissolution of minerals and dolomitization. The study of diagenesis in rocks is used to understand the geologic history they have undergone and the nature and type of fluids that have circulated through them. From a commercial standpoint, such studies aid in assessing the likelihood of finding various economically viable mineral and hydrocarbon deposits. The process of diagenesis is also important in the decomposition of bone tissue.

    続成作用(ぞくせいさよう、diagenesis)は堆積物が固まって堆積岩になる作用で、以下のような2つの方向の作用がある。 物理的続成作用砕屑物がを受け、粒子間の隙間が詰まったり、粒子間の水が排水に伴って抜けたりする圧密現象(コンソリデーション)と呼ばれる物理的作用を中心とする。化学的続成作用地下水に溶け込んだ成分(炭酸カルシウムや二酸化ケイ素など)が晶出し、長期間を経て、粒子間結合部およびその周辺に化学生成物を析出し、固結力を高める(:セメンテーション)作用等。 物理的作用と化学的作用は堆積終了と同時にスタートするが、初期は主に圧密に伴う物理的作用が支配的で、その終了の後、数万年もの長期にわたって化学的続成作用が続く。なお、化学的作用は、固結した堆積岩が掘削などによって表層に露頭し、乾湿繰り返しや凍結融解などの風化作用を受けると次第に消失して強度低下をもたらし、さまざまな工学的問題を引き起こす場合がある。

    (Source: http://dbpedia.org/resource/Diagenesis)

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